A number of percutaneous intravascular procedures have been developed for treating stenotic atherosclerotic regions of a patient's vasculature to restore adequate blood flow. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). In PTA, a catheter, having an expandable distal end usually in the form of an inflatable balloon, is positioned in the blood vessel at the stenotic site. The expandable end is expanded to dilate the vessel to restore adequate blood flow beyond the diseased region. Other procedures for opening stenotic regions include directional atherectomy, rotational atherectomy, laser angioplasty, stenting, and the like. While these procedures have gained wide acceptance (either alone or in combination, particularly PTA in combination with stenting), they exhibit certain significant disadvantages.
A particularly common disadvantage with PTA and other known procedures for opening stenotic regions is the frequent occurrence of restenosis, which refers to the re-narrowing of an artery after an initially successful angioplasty. In the absence of stenting, restenosis afflicts approximately up to 50% of all angioplasty patients and is the result of injury to the blood vessel wall during the lumen opening angioplasty procedure. In some patients, the injury initiates a repair response that is characterized by smooth muscle cell proliferation referred to as “hyperplasia” in the region traumatized by the angioplasty. This proliferation of smooth muscle cells re-narrows the lumen that was opened by the angioplasty within a few weeks to a few months, thereby necessitating a repeat PTA or other procedure to alleviate the restenosis.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation during angioplasty, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation following angioplasty, stenting of the region, and other procedures. While these proposed strategies have enjoyed varying levels of success, none has been proven to be entirely successful in substantially or completely avoiding all occurrences of restenosis and hyperplasia.
As an alternative or adjunctive to the above mentioned therapies, the administration of therapeutic agents following PTA for the inhibition of restenosis has also been proposed. Therapeutic treatments usually entail pushing or releasing a drug through a catheter or from a stent. While holding great promise, the delivery of therapeutic agents for the inhibition of restenosis has not been entirely successful.
Of particular interest to the present invention, the use of radiation and “radioactive” stents for inhibiting vascular hyperplasia has been proposed. Radioactive intraluminal endovascular stents prevent neointimal hyperplasia by nonselectively killing dividing cells. The long term consequences of radiation and other stent-delivered therapies on normal heart and on non-cardiac tissue are unknown. Beta particle emitting radioisotopes attached to stents, such as phosphorus-32, deliver 95% of the radiation dose within 4 mm of the stent edge and the radiation dose decreases to less than 1/1000 of the original dose at five months post implantation. However, the depth or distance (4 mm) into tissue by beta emitters is excessively deep because the majority, if not all the abnormal changes occur in diseased coronary arteries and specifically vulnerable plaque are within a depth of less than 0.33 mm.
For these reasons, it would be advantageous to provide improved medical devices to accurately deliver radiation only to desired areas in order to more effectively and safely treat hyperplasia in the vasculature following angioplasty and other interventional treatments. It would be further desirable if the improved methods and devices were useful for treating other luminal hyperplasia and neoplasia, including tumors and other neoplastic disease which can occlude and otherwise interfere with the functuality of body lumens. A radioactive stent that is used therapeutically to prevent restenosis and that has the additional benefit of being able to be imaged using a gamma camera would be of clinical utility in determining the position of the stent, to determine radioactive dosimetry and decay and potentially to reveal an internal imaging of soft plaque and hard plaque material. The present invention now provides such improved devices and treatment methods that meets the needs in the art.